Monday, 20 April 2015

Thorn Sherpa / Raven Forks Review - Intro

These are the third set of Thorn Forks I have purchased, and despite their lack of disc brake bosses, I continue to buy Thorn forks for their incredibly long steerer tube, which give the most glorious upright ride, on any standard mountain bike frame. With an un-cut 400mm steerer riding a bike is a joy, with views over hedges and fences, and no uncomfortable bending of the neck to look where you are going.

Thorn Sherpa / Raven Forks Review - Thorn Write Up

This is the heavy duty touring fork option for Sherpa Mk3 and Raven frames it is for 26” wheels (559)

This fork has clearance for 2.15” tyres.

It measures 370mm from axle to crown race seat and has a 400mm long steerer

It has M5 stainless steel bosses for the direct and secure fitting of mudguards as well as bosses for lo-loader carriers

The fork has V brake bosses on the front of the blades, at the perfect height for 559 rims

It uses a cast crown which has an M6 thread for a dynamo lamp boss

The blades are manufactured by Reynolds in “SUPER TOURIST” gauge and have a comfortable, tight radius bend with safety dropouts.

These forks can carry up to a maximum of 7.5Kg on each side

Thorn Sherpa / Raven Forks Review - Off Bike Pictures

Thorn Sherpa / Raven Forks Review - On Bike Pictures

Thorn Sherpa / Raven Forks Review - Verdict

If you need a fork for touring or any type of cycling where comfort and versatility are more important than looks, then look no further. Its a shame there are no disk brake mounts (perhaps look to the Surley Disc Trucker Forks), but V brakes are OK, and a sturmey archer drum brake (such as XL FDD) can always be used for low maintenance option.

If you have suspension forks then you may wish to opt for one of thorns "double crown" forks which gives some level of suspension correction (Thorn Mt Tura for example).

Full price these forks are £100, sometimes thorn forks come up in the sales, so if you are patient then maybe you can find a pair for cheaper, I got these for £60, and 2 years ago I managed to get some carbon forks, which these replaced, for £50.

Sturmey Archer Drum Brake Service - Intro

After 3 years (3000 miles) of maintenance free braking my XL-FDD Drum Brake had developed a small squeak, this happened when applying the brake. It was not a typical brake squeal, more a little squeak when the cam pivot arm (see below pictures for names) was moved.

So reluctantly I decided to open the brake up and see what was going on inside. This procedure could apply to any of the following models:

Sturmey Archer Drum Brake Service - Open Up

First off I removed the Cam Lever Arm, which I would advise you to leave in place / attached. You will need to wiggle this later on to work in some grease.

The modern Sturmey Archer Drum Brakes have cartridge bearings, so for those of you that are used to bearing cones etc. the procedure is far more simple. Holding on to the "anchor arm" (see below) undo the nut, and remove it from the axle. The brake plate assembly should now slide off.

Sturmey Archer Drum Brake Service - Clean & Lube

In side you will see that the brake pads are firmly attached to the brake plate assembly, the pads do not need to be removed for cleaning, simply use an automotive brake cleaner which you can pick up from your local motor factors (uni part for example) for £4 a can.Whilst I would say it is OK to blast the shoes with cleaner, be careful not to get any on the bearings in the hub drum, instead spray some on a cloth and wipe around the inside of the drum.

Sturmey Archer Drum Brake Service - Lube

Next up we need to lube the cam that spreads the shoes (see below picture), you will need to wiggle the cam lever arm (first picture on page), so you can poke some grease in the the areas where it is needed. Try not to get any grease on the shoes.

Next apply a little light oil to the upper pivot, see below.

Sturmey Archer Drum Brake Service - Put Back Together

This is the reverse of taking apart! The only thing to watch out for on the hub dynamo models is that the power outlet is lined up to where it was before taking apart. This is a little tricky because as you tighten the nut on the brake side the power outlet will rotate on the other side, but after a few goes no doubt you will get it right.

Thursday, 9 April 2015

How to Replace a Worn Out Bicycle Rim - Intro

Many bike come with rim brakes, and whilst cycling in clean conditions will result in very long rim life, muddy or dustry conditions can lead to rims becoming worn out. Frequently off road use with rim brakes may wear out a rim in less than a year, for most though a rim will last 2 or 3 years.

Many rim nowadays have a wear indicator, a small grove or channel that run around the rim, if this is no longer visable, then chances are you will need to replace your worn out rim.

How to Replace a Worn Out Bicycle Rim - ERD

To make things easier for yourself and to avoid having to replace spokes you will need to buy a replacement rim which is the same size (or netter still buy the same rim make and model). The most important measurement is the ERD (Effective Rim Diameter). To find the ERD of you rim simple google its make and model with "ERD" after the search term. For example "Mavic EX721 ERD". And hopefully you will find out that way. Rememebr rims can come in 20", 26", 29" sizes, so be sure you are looking at the right size.

If you can not find a measurement on the web then take a tape measure and measure the maximum internal diameter of the rim and add about 4mm. This does not always give a very accurate measurement but I have done this 2 or 3 times with no problems.

So you have found your ERD, now look for a rim with a similar ERD, I replaced a factory stock alloy rim (ERD 551) with a Sun Rhyno Lite XL Rim (ERD 544), so you can go 3, 4 or 5 mm out, and still be OK.

How to Replace a Worn Out Bicycle Rim - Replace

I leant this method from a book a had a few year ago, and it a excellent way to replace a rim, as there is no need to worry about spoke lacing errors (putting spoke in the wrong hole).

First off line up the holes where the inner tube valve pokes through. Make sure to have some tape or zip ties handy.

Next fasten the rims together using some zip ties or tape. 3 points around the rim is normally enough. Then as in the above picture start to swap the spokes from the old rim to the new rim.

Take the top spoke from each crossed pair and move it upwards to the new rim, work around the wheel moving up all of the top spokes on that side on to the new rim. Do up the nipples so 3 threads are showing, you need to leave them a bit lose loose, especially on a rear wheel because other wise the "dish" will not form properly.

After you have moved all of the top spokes on one side of the rim, flip the whole lot over and do the same to the top spokes on the other side. Then repeat this process for all of the lower spokes, and hey presto, all of the spokes should be in the new rim, and you can detach the old rim.

Now go around and tighten the nipples so no threads are showing. No head for the grage and put the wheel in the bike.

How to Replace a Worn Out Bicycle Rim - Truing and Tensioning

With the wheel in the bike (vertical drop out preferable here) measure the distance from the braking surface to the bike frame, do this on both sides. You will need to keep doing this during gradually tightening the spokes to make sure the wheel is centred in the frame.

Spin the wheel in the frame it will probably wobble all over the place. At this stage you can gauge the wobble by eye. But later on you may wish to place something next to the rim (zip tie or rim brake) so as to gauge the wobble more accurately.

STEP 1

If it wobbles to the left tighten a right hand spoke, and vis versa. Just 1/2 a turn at a time, if its a big wobble tighten 2 or 3 spokes on the same side in the area of that wobble. Do this until the wheel is fairly straight with perhaps 5mm - 10mm of wobble in either direction.

STEP 2

Then start to increase the spoke tension. Tighten ALL of the spokes half turn working around from the valve hole. You do not have to start at the valve hole, but this makes it a lot easier, as it acts as a point of reference.If at this points some spokes seem at lot tighter than other then don't tighten them.

Keep repeating the steps 1 and 2 left until the wheel solid and all of the spokes are firmly tight. You can purchase a spoke tensioner all I have never used one.

BIG GAP ON LEFT - TIGHTEN LEFT HAND SPOKES

TOO CLOSE - TIGHTEN RIGHT HAND NIPPLE

WELL DONE ME - JUST RIGHT

It is important to realise that at any point you feel things are not going well, just slacken off all the spokes to 3 threads showing and start again. The only game killer is if you over tighten a spokes and strip the thread.

For you first go choose a strong rim, I would assume these will account for you error better than a weaker rim.

Rims vary in width up to about 30mm is OK for use with rim brakes, but you may struggle to adjust them nicely with wider rims.